*Bill Mahanna, Ph.D., Dipl ACAN, is a collaborative faculty member at Iowa State University and a board-certified nutritionist for DuPont Pioneer based in Johnston, Iowa. To expedite answers to questions concerning this article or to submit ideas for future articles, please direct inquiries to Feedstuffs, Bottom Line of Nutrition, 7900 International Dr., Suite 650, Bloomington, Minn. 55425, or email [email protected]
LAST month, I was fortunate to participate in an international symposium on feed efficiency in dairy cattle. It was organized by the Netherlands Centre for Animal Nutrition, which consists of researchers from Wageningen University, Lelystad Research Center and the Veterinary College at the University of Utrecht.
This conference drew 234 participants from 21 countries, which allowed for an exciting exchange of ideas during presentations and, just as importantly, over many side conversations held during the breaks.
In this month's column, I decided to share some of the key learnings I took away from this conference and give insight as to what the rest of the world is thinking regarding the feed efficiency of dairy cattle and their effects on the environment.
Theun Vellinga, a senior scientist at Wageningen UR Livestock Research at Lelystad, presented an interesting overview of the global impact of cattle numbers and industry segmentation. He showed data on the static nature of cattle numbers in Europe, North America and Oceania yet significantly increasing numbers in South Asia and Central and South America.
This led him to present a two-pronged view of the ruminant livestock sector, divided into industrial/specialized and smallholder (Vellinga, 2013).
The industrial/specialized sector optimizes animal nutrition, and all activities are focused on animal performance. This sector typically raises its own high-quality crops, displaying high energy input and a high greenhouse gas (GHG) profile.
The smallholder sector is on a smaller scale with multifunctional farms; the system as a whole is optimized, and animal nutrition competes with other production goals.
The variation is these livestock sectors was reflected in livestock diets, where feedstuff digestibility can range from 45% up to 80% (Vellinga, 2013).
Mitigation strategies to improve feed efficiency and reduce the GHG impact on the environment (methane, nitrous oxide and carbon dioxide emissions) for these two sectors were discussed in relation to milk output of the animal.
Vellinga suggested that the growing smallholder sector needs to address manure management, grazing management, feed availability and digestibility and animal health, while the industrial/specialized sector needs to focus on new technologies in feeding and additives, genomic opportunities and system innovations in energy usage.
Feed nitrogen utilization
Chris Reynolds, director of the Centre for Dairy Research at the University of Reading in the U.K., presented an overview of approaches to improve the efficiency of feed nitrogen utilization.
Reynolds noted that excess crude protein has historically been fed because it provided a safety factor in the diet and generally increased feed intake — especially for diets containing lower-quality forages — and, until recently, there had not been any cost restrictions in terms of environmental impact. The final reason has changed significantly due to nitrate leaching from urine and feces becoming an environmental concern not only in cow-dense areas like the Netherlands but also in North American environments like the Chesapeake Bay watershed.
Nitrogen excretion has an effect on air quality and GHGs due to gaseous losses as ammonia and nitrous oxide (Reynolds et al., 2013).
The question becomes how much to reduce dietary protein without sacrificing economic losses. Reynolds discussed work done with rumen-protected methionine or methionine analogs given that methionine is considered the first limiting amino acid in lactating dairy cows. However, to date, consistent success with individually supplemented amino acids has been limited, presumably due to the lack of other limiting amino acids in the diet.
Reynolds referenced a recent study (Hague et al., 2012) in which balancing the supply of methionine, lysine, histidine and leucine increased both milk yield and nitrogen use efficiency. Another issue that needs managing is the variability in forage quality that limits the effectiveness of dietary strategies to precisely feed prescribed amounts of essential amino acids for absorption (Reynolds et al., 2013).
There is likely an important role of synchrony of dietary energy and protein sources to maximize the efficiency of microbial protein synthesis and minimize ammonia absorption from the rumen. While Reynolds admitted that the applied feeding studies attempting to prove the value of "synchronous" feeding have been disappointing, more work is needed in this area.
It was also suggested that another important factor determining post-absorptive nitrogen use efficiency is the rate of milk protein secretion by the mammary gland relative to the rate of absorption of individual amino acids (Reynolds et al., 2013). This is because catabolism of essential amino acids by the liver and other body tissues is largely determined by the extent to which they are absorbed in excess of requirements of the mammary gland (Reynolds, 2006).
Finally, most studies looking at the manipulation of dietary protein have been short-term studies. Reynolds and his research team at the University of Reading have secured funding to begin to look at the long-term effect of lower protein levels on dairy cow production, fertility, health, longevity and profitability.
Jan Dijkstra, associate professor with the Animal Nutrition Group at Wageningen University and an adjunct professor at the University of Guelph in Ontario, presented some interesting data on maintenance requirements.
Maintenance requirements are considered to be fixed, explaining the dilution effect of increased production increasing feed efficiency. The liver and gut account for a large part of nutrient metabolism and contribute to maintenance requirements and nutrient delivery to various body tissues and organs (Dijkstra, 2013).
Dijkstra compared energy studies done 30-50 years ago with more current data and suggested that modern, higher-producing cows do have a higher feed efficiency related to dilution of maintenance, but they also have 20-40% higher maintenance energy requirements than currently used estimates. This is due to a body composition change between traditional and modern cows in terms of energy required for visceral (intestinal, splanchnic) tissues.
Dijkstra also said the efficiency of metabolizable energy to milk energy had been reported to be higher with high-genetic merit cows, but when correcting for tissue energy retention, there does not seem to be a significant difference in this efficiency between high- and low-genetic merit cows.
Dijkstra concluded that improving feed efficiency and reducing methane output required an interdisciplinary, fundamental approach and that direct methane inhibition through the use of dietary lipids, nitrates or tannins typically does not improve feed efficiency. His advised approach to improve feed efficiency and reduce methane emission intensity is to increase milk production levels and improve forage quality (Dijkstra, 2013).
Cow health, efficiency
Ad van Vuuren, a senior scientist at Wageningen UR Livestock Research at Lelystad, presented a compelling argument that improved cow health directly improves feed efficiency by maintaining production and reducing the nutrient cost required for recovery from metabolic or infectious disease.
Van Vuuren discussed the role of excess adipose tissue mobilized during the transition period and the incidence of early-lactation metabolic disorders. He questioned if selection for sires with daughters displaying high milk production in the first 100 days of lactation had inadvertently led to selection for an increased capacity for fat mobilization.
To maintain production and optimize feed efficiency, van Vuuren suggested that preventing metabolic disorders should not focus solely on feeding strategies to improve the supply of energy and nutrients but also on strategies to support fat metabolism and/or prevent massive fat mobilization such as the supplemental use of niacin, L-carnitine and choline.
The relationship between extreme changes in fat metabolism and a reduction in the immune system was also discussed. Adipose tissue can release cytokines (adipokines), stimulating the formation of acute-phase proteins and resulting in "metabolic inflammation." Increased levels of these cytokines and acute-phase proteins have been reported in cows diagnosed with a high liver fat content.
Improving cow health, leading to better feed efficiency, requires professional transition management that goes beyond improving feed intake to managing the relationship among fat mobilization, metabolic diseases and the immune response (van Vuuren, 2013).
The Bottom Line
Improving feed efficiency and reducing the environmental impact of nitrogen leaching and GHG emissions are clearly global priorities. This international conference provided a good overview as to how higher production (to dilute maintenance costs), along with attention to forage quality, protein supplementation strategies and managing metabolic disorders, can go a long way toward achieving these goals.
Dijkstra, J. 2013. Nutrient losses during digestion and metabolism. Proceedings of International Dairy Nutrition Symposium on Feed Efficiency in Dairy Cattle. Nov. 21. Wageningen, Netherlands. p. 43-52.
Hague, M.N., H. Rulquin, A. Andrade, P. Faverdin, J.L. Peyraud and S. Lemosquet. 2012. Milk protein synthesis in response to the provision of an ideal amino acid profile at two levels of metabolizable protein supply in dairy cows. J. Dairy Sci. 95:5876-5887.
Reynolds, C.K. 2006. Splanchnic metabolism of amino acids in ruminants. In: K. Sejrsen, T. Hvelplund and M.O. Nielsen (eds.). Ruminant Physiology, Digestion & Metabolism & Impact of Nutrition on Gene Expression, Immunology & Stress. Wageningen Academic Publishers, Netherlands p. 225-248.
Reynolds, C.K., L.A. Crompton, J.A.N. Mills, C.E.S. Barratt and D.G. Barber. 2013. Improving the efficiency of feed nitrogen utilization. Proceedings of International Dairy Nutrition Symposium on Feed Efficiency in Dairy Cattle. Nov. 21. Wageningen, Netherlands. p. 53-62.
Van Vuuren, A. 2013. Dairy cow health management for improved longevity and feed efficiency. Proceedings of International Dairy Nutrition Symposium on Feed Efficiency in Dairy Cattle. Nov. 21, 2013. Wageningen, Netherlands. p. 65-77.
Vellinga, T. 2013. Dairy production in a global perspective. Proceedings of International Dairy Nutrition Symposium on Feed Efficiency in Dairy Cattle. Nov. 21. Wageningen, Netherlands. p. 7-10.